The invention relates to an ignition device for a motor unit comprising an internal combustion engine, in particular for a motor unit with a two-stroke engine of a portable hand-held power tool. The internal combustion engine of the motor unit comprises a piston, a combustion chamber with a spark plug, a crankshaft that is driven in rotation by the piston, an intake port for supplying combustion air into the combustion chamber, an exhaust for removing combustion gases from the combustion chamber, as well as a signal generator driven in rotation by the crankshaft and attached to the motor unit and emitting for one crankshaft revolution sequential alternating voltage signals to an ignition unit that triggers a spark at the spark plug at a preselectable timing.
Modern internal combustion engines as they are used in connection with hand-held portable power tools such as motor chain saws, trimmers, cut-off machines, blowers or similar devices are controlled by ignition devices that, in addition to the alternating voltage signal for high-voltage supply of a spark plug, must have an ignition trigger for triggering ignition that is to be arranged at approximately 40 degrees before top dead center. The ignition trigger must be attached circumferentially relative a revolving pole wheel on the crankcase in a precise rotational position wherein, in mass production of such engines, fluctuations with regard to mechanical arrangement of the ignition trigger occur that can impair ignition timing. Moreover, the constructively fixed arrangement of the ignition generator, ignition module as well as engine speed sensor is troublesome because these parts are often arranged within the cooling air passage at the fan wheel and occupy space in the cooling air passage. This can cause cooling problems so that the cylinder is thermally stressed to a greater extent.